Energy transmission devices of this type are used to transmit electric energy from a stationary current lead of a primary circuit to the secondary circuit of a mobile consumer Possible applications are, for example, in industrial assembly conveyor systems or passenger vehicles.
In these situations the contactless inductive energy transmission is advantageous. It avoids the use of sliding contacts that are prone to wear. Moreover, difficulties are avoided with respect to protecting exposed lines when installing the current lead on the floor and poor contacting due to contaminated lines. By installing the lines in the floor, ceiling or walls, the danger of contacting of previously conventional current-carrying rails can be eliminated.
Known systems can be problematic in the event of simultaneous use by several consumers. The cause of this is the interaction between consumer and the stationary current lead.
In normal operation, an alternating current flows through the primary circuit. The secondary circuit of the consumer forms an oscillating circuit that is coupled with the primary circuit via the coil of the oscillating circuit and resonates at the frequency of the primary circuit.
If a consumer is drawing little energy from the primary circuit, then this means an increased impedance in the load circuit. This impedance is mirrored in the primary circuit by the transformer effect. Due to this increased impedance in the primary circuit, the flow of current through the primary circuit is impeded and thus the supply for other consumers is reduced. If no energy is used, then the coil of a consumer can completely block the flow of current in the primary conductor. Thus, further consumers cannot be operated independently of the first consumer and not individually regulated in their power consumption.
One attempt to overcome this problem can be found in the patent PCT 92/17929. In this case, an electric or mechanical decoupling device is installed on each consuming device. However, this concept requires that, for example, a large-scale decoupling device, e.g. a hydraulic piston, be transported on consumer vehicles.
WO 93/23909 describes a system in which the primary circuit has guidance loops arranged behind one another in the direction of travel. These guidance loops are bypassed and thus not traversed by current if there is no consumer in the area of its electric field. However, this concept does not offer a solution for the operation of several consumers since, in this case, parts of lines not used are not to be disconnected but, instead, several consumers are to be supplied in spite of a blocked primary line.